Is he aware of these periods and does he recognize it as an issue?...I mean one reason I am afraid of getting into a relationship is because I am afraid when my depression and other issues really get to me it would cause trouble with the relationship. But yeah if he recognizes it is he getting any help or therapy? If he is more reasonable when he's in a better state perhaps having a serious conversation with him about it at that point would be a good idea...let him know you care about him but its difficult to deal with it when he acts that way and its concerning. Perhaps getting counseling yourself could be useful as they might have some advice on how to deal with this....or maybe both of you going to like couples counseling could help. But it takes two people he'd have to be willing to put in some effort to just like you for things to work out.

But yeah that sounds more like depression issues than psychotic issues.....I get like that to and I hate it because I know it can be hard for others to deal with.